Direct contact gas-liquid heating devices are generally known in the prior art. In a typical device, fuel is burned in a combustion chamber to produce heated gases which then bubble up through a liquid medium giving up a portion of their heat to the medium. Some known configurations locate a combustion chamber or burner can in the liquid medium. A burner is located within the combustion chamber and a mixture of fuel and air is piped into the burner and ignited. In this configuration radiation heat is directly absorbed by the liquid medium, which also serves to cool the combustion chamber or burner can.
In direct contact heaters, it is desirable to introduce the heat gases into the liquid medium at the lowest possible level to provide a longer path for the bubbles to travel and hence more efficiently transfer the heat from the gas to the liquid medium. Some configurations accomplish this by inverting the burner within the combustion chamber. The combustion gases flow to the bottom of a surrounding tank and bubble upwardly through a liquid medium in the tank. However, there is a tendency for the liquid medium to sump back through the distribution system and drown the burner when the heater is shut off in this construction. This is especially a problem in applications which require the heater to cycle off and on periodically, such as in a home heating system or hot water heating system.
There are some configurations which utilize an upwright flame, but these systems are not nearly as successful in conveying the heated gases to the bottom of the liquid medium for distribution and bubbling. These systems normally depend upon maintenance of the liquid medium level within close tolerances; low enough to prevent the sumping as previously discussed, but high enough to keep the bubble distribution structure in contact with the liquid medium. This structure is less efficient since the liquid level must be lower than the top of the burner.
There are other configurations which utilize more than one liquid medium, by pumping a second liquid through pipes in the direct contact heater tank. These are not nearly as efficient as devices using one liquid medium because the second liquid medium is in indirect thermal contact through the walls of the pipes with the first liquid medium. This reduces the rate of heat exchange.
The efficiency of direct contact gas liquid heaters is generally a function of the size of the bubbles and the degree of mixing obtained before the gas escapes the medium. Obviously, the smaller the bubbles and the greater the degree of mixing, the higher the efficiency and the exchange of heat from the gases to the medium. In an ideal direct contact heater, the temperature of the gases leaving the medium would be the same as the temperature of the medium.
Applicant has succeeded in developing a device which maximizes efficiency of heat exchange while avoiding the problems associated with the structure used previously. Applicant's device may utilize one liquid medium, an upright flame and burner, a submerged combustion chamber and gas distribution system, and a bubble distribution array which distributes the gas bubbles into the medium at the lowest possible level. A liquid medium level raising and lowering structure may preclude sumping of the medium when the burner is shut off.
Applicant's invention can be more fully understood by referring to the following drawings and the explanation contained in the preferred embodiment.